Download Diapositiva 1

Cluster of galaxies and large area survey
&
Wide-field X-ray telescopes
Sergio Campana
INAF - Osservatorio Astronomico di Brera/INAF - Via Bianchi 46 – 23807
Merate (Lc) – Italy
Outline
• Dark energy probe: needs for a large area survey
• Wide-field X-ray polynomial optics for imaging applications: short review of the
concept
Mainly based on Panoram-X proposal and NASA white papers (Haiman et al.
2005 and Vikhlinin et al. 2005) and final JDEM proposal (Bautz et al. 2006).
but…
I am not an expert in clusters of galaxies and large scale structures
I am not an expert in mirror manufacturing
… so I will try to be short
Why is the
universe
expansion
accelerating?
What is DE made of?
(73% of our universe is made of DE!)
Probes
Now
Future
CMB
WMAP
Planck
Supernovae
HST
SNAP
Cluster ofofgalaxies
Clusters
galaxies
X-ray satellites
Dedicated survey?
??
Cluster power
spectrum and X-ray
luminosity function
(Schuecker et al.
2003; Boehringer
2006)
Evolution of
the cluster
temperature
(Henry 2004)
COMPLEMENTARY
APPROACHES
Evolution of
the cluster
gas mass
(Vikhlinin et
al. 2003;
2006)
Constancy of the
cluster
baryon
fraction
(Allen et
al. 2004)
Cluster Survey
105 clusters
Need to study the brightest
fraction of clusters to calibrate
relations
Constrain the equation of state of
Dark Energy, (i.e. understand what is it!)
w(z)=w0 + wa z/(1+z)
Better than high-z SNe or weak lensing surveys
Cluster survey in context
Survey simulated image
Simulation of a 2,000 s, 1.7 1.7 square degrees field observation. There are ten clusters with fluxes
ranging in 0.59  10-13 erg s-1 cm-2 (#1-#10). Note that all background points in the image correspond
to sources. All clusters are detected as extended with high significance.
Point-source limit
Side products:
X-ray background
AGN studies
Starts in our Galaxy
Cataclismic variables
What do we need? Theory
What do we need? Practice
Field of view
Orbit efficiency
Vignetting efficiency
: 1.4 square degrees
: 70%
: 70%
7-14,000 pointings
Survey area
: 10-20,000 square degrees (slowly drifting satellite)
Extended source detection : 30-50 counts
Allocated time
: 9-12 months
Flux limit for ext. sources : 2-5 x10-14 erg cm-2 s-1
MINIMAL REQUIRMENTS
Area
: 10,000 square degrees
Extended source detection : 30 counts
Allocated time
: 9 months
Flux limit for ext. sources : 5 x10-14 erg cm-2 s-1
Need 1,825 cm2
What about angular resolution
Concerning clusters of galaxies 15 arcsec HEW (over the entire
field of view) are enough
…but for survey purposes the lower the better (Goal: 5 arcsec HEW
over the entire field of view)
How can we obtain these features?
X-ray optics with polynomial profile
• Mirrors are usually built in the Wolter I (paraboloid-hyperboloid) configuration
which provides, in principle, perfect on-axis images.
• This design exhibits no spherical aberration on-axis but suffers from field
curvature, coma and astigmatism, which make the angular resolution to degrade
rapidly with increasing off-axis angles.
• More general mirror designs than Wolter's exist in which the primary and
secondary mirror surfaces are expanded as a power series.
• These polynomial solutions are well suited for optimization purposes, which
may be used to increase the angular resolution at large off-axis positions,
degrading the on-axis performances (Burrows, Burgh and Giacconi 1992)
• A trade-off of the whole optics assembly of a wide-field telescope can further on
increase the imaging capabilities off-axis of wide-field polynomial optics
The wide-field polynomial optics concept was extensively studied as
a part of the WFXT mission concept (OAB, CfA, Univ. of Leicester)
Some historical remarks on WFXT-like missions
• 1992, Burrows, Burg and Giacconi investgate the possibility of using polinomial mirror
configurations to get X-ray optics with a corrected PSF onto a large FOV
• 1995: WFXT small satellite proposal to NASA (PI R. Burg, J. Hopkins Univ, CfA, OAB)
• 1997-98: WFXT proposal and Phase A to ASI in the context of the small satellites program
(PI G. Chincarini, OAB + large part of the Italian AE community, CfA, Leicester Univ.)
• 2000: Panoram-X mission proposal to ESA in the context of the F2-F3 program
• 2001: Conconi & Campana paper (A&A 2001) improving mirror design
• 2003: ASTER-X concept (OAB in collaboration with NASA/GSFC) in view of the probeEinstein program (never started), further mirror design improvement
• 2005 NASA Call for white papers on Dark Energy exploration; two proposal based on the
Panoram-X concept; also ESA mention in the Cosmic Vision booklet the need of a similar
mission, merged into a single proposal DECS (PI Bautz/MIT – including OAB scientists).
WFXT (ASI feasibility study 1997-1998) – Polynomial mirrors
Tests @ PanterMPE & Marshall
XRF
WFXT (epoxy
replication on SiC
carrier) – Ø = 60 cm
Focal Lenght = 300 cm
HEW = 10 arcsec
Citterio et al. 1999, SPIE 3766 198
The Panoram-X mission
• proposed to ESA in 2001 in the context of the F2-F3 Mission
Program
• in practice, it is the same WFXT concept scaled up in FL (3.5 vs. 3 m) and # of
mirror shells (50 vs. 24)
• SiC mirror shells with diameter ranging from 70 to 21 cm, total mirror height of 28
cm and max wall thickness= 1 mm. Predicted HEW of 10 arcsec over a field radius
of 30 arcmin (including profile and integration errors)
• X-ray camera made of an array of nine CCDs arranged in an inverted pyramid
that matches the focal surface of the mirrors. Each device is a 600x600 pixel front
side illuminated frame store with pixel size 40 m corresponding to 2.4 arcsec in
the focal plane. Energy resolution provided by the CCDs is E/E 10% at 1.5 keV
Panoram-X Effective Area
E = 1 keV
The ASTER-X (ASTronomical ExploreR for X-rays) mission
• Study performed in view of a Probe-Einstein class
mission (2003 year) under request of NASA/GSFC
• Baseline: an X-ray telescope able to provide 1300
cm2 at 1.5 keV and 650 cm2 at 4 keV of effective
area, with an angular resolution (HEW) better than 5
arcsec over a FOV of 30 arcmin
• #2 mirror modules, 12 monolithic shells
• Focal length 7 m
• Max, Min diameters: 1020 - 690 mm
• Max, Min height: 485 mm, 330 mm
• The focal plane has a curvature radius of 280 mm
Wall thickness: 10 mm constant
 if made in ZerodurTM  423 Kg per module
 if made in foamed SiC  a factor 3 less (at least!)
Optical axis
ASTER-X: theoretical performances of the design
HEW of the order of ~3 arcsec on
most of the FOV, reaching a value
of ~5 arcsec at 30 arcmin off-axis
On-axis effective area: 800 cm2 @1
keV/ module
The reflecting coating is Ir + a Carbon
overcoating to enhance the soft X-ray
reflectivity
ASTER-X off-axis vignetting
ASTER-X feasibility
• Mirror shells twice longer than
WFXT: it’s a much more favorable
conditions to reduce slope errors
• Focal length similar to that used for
Chandra and XMM
ASTER-X
• Mass-to-area ratio just ~20 % than
ROSAT if ZerodurTM is assumed
Difference (rms) between Wolter
I and polynomial profiles
Mirror
shell
Front
surface
Rear
surface
N° 1
2”.49
0”.46
N° 12
2”.14
1”.28
Typical rms surface values measured for ROSAT:
 0.5 arcsec
Adding 0”.5 rms value to our nominal polynomial
profile, we find that the HEW values increase on
average less than 1” and remain always below 5”.
Possible implementation of a cluster survey mission based on the
previous concepts
Possible options:
• ready-off-the-shelf & not (too) expensive mirror technology (XMM-like with
refined design based on Ni) to meet the moderate angular requirement (15-25
arcsec HEW).
• use of the same technology and input requirement of wide FOV high imaging
mission (ASTER-X like based on ZERODUR, i.e. glass) to have a 5-10 arcsec
HEW. To have an effective area of 1800 cm2 this implies a total mirror weight
of  800 kg x Tsurvey/(9 months)
• new technologies under study like slumped glass (HEW  5-10 arcsec and
weight  250 T9 kg) or already proven SiC (HEW  10-20 arcsec and weight
 200 T9 kg)
Conclusions
Theory: strongly constrain Dark Energy equation and deep survey of the
AGN population
Large area cluster survey >10,000 square degrees
Effective area >1,800 cm2 and/or survey time > 9 months
Mean HEW < 15 arcsec
Caveats (to have 5 arcsec HEW)
Ad hoc mirror assembly (mirrors with different lenghts)
Ad hoc focal plane assembly (inverted pyramid)
Practice: feasible from the point of view of mirrors. Angular resolution
depending on mirror weight
My personal view
Microcalorimeters science:
• WHIM absorption
• WHIM emission
CCD science:
Science drives
• Dark energy
• Outskirts of clusters
• GRB
• Superbursts
• Type I X-ray bursts
Vision
Single telescope (1800 cm2 5-10” HEW)
Small FOV microcalorimeter (< 5’x5’)
CCDs around (> 30’x30’, possibly 40’x40’)
Fast response and GRB/superburst location capabilities